Binocular range estimating periscope operating on the coincidence principle



y 13, 1947- J. M. sTRANG 2,420,506

. BINOCULAR RANGE ESTIMATING PERISCOPE OPERATING ON THE COINCIDENCEPRINCIPLE Filed May 25, 1943 Job: Mar/m 07m I ventor 5am W fimmu) Aftorney Patented May 13,1947

UNITED STATES- PATENT; oF-Ficn BINOCULAR RANGE ESTIMATING PERI- SCOPEOPERATING ON THE' COINCIDENCE'R PRINCIPLE 1 John Martin Strang, Glasgow,Scotland,.assignor I to Barr & Stroud, Limited,.Glasgow,' ScotlandApplication May 25, 1943, Serial No": I488,448J-' In Great BritainAugust 14,",1940- a 1 Claim. (01. 88- 2.?)

the twobeams of light which-are to form thetwoim'ages are-directed on toopposite sidesof an obliquely disposed light transmitting and refleetingscreen where each beam is partly transmitted through the screen andpartly reflected at the screen, the reflected part of one beam and thetransmitted part of the other beam leaving the screen together andpassing into the eyepiece of the instrument. The one of these parts formthe one image and the other forms the other image. The practice is forthe screen surface to be partially metallised, usually aluminised orsilvered.

A disadvantage of the overlapping image type of instrument in itsexisting form is the loss of light, the part of one beam transmitted atthe screen and the part of the other beam reflected at the screen beinglost.

The object of the present invention is to provide for the utilisation ofthat portion of the light which is thus ordinarily lost.

Under this invention, the instrument is provided with two eyepieces, onefor each eye of the observer, and is so constructed that those portionsof the two beams which are not directed to one of the eyepieces from thetransmitting and reflecting screen are directed therefrom to the othereyepiece, so that, apart from transmission losses, the whole of thelight of the two beams reaches the eyes of the observer.

In carrying the invention into practice, there is used a prismcombination embodying a trans- :mitting and reflecting screen and asecondary refleeting system which latter intercepts those portions ofthe two beams which are not directed :from the screen into the oneeyepiece and directs them into the other eyepiece.

The optical paths should be so arranged that the focal planes aresubstantially at equal distances from the base axis of the instrument.

The invention will now be described with ref- .erence to theaccompanying drawings, in which:

Figures 1 and 2 are two diagrammatic views showing .the applicationoftheinventionlto' an.

inclinometer, and

Figure 3 shows the application of the invention to -a range-estimatingperiscope.

Referring to Figures .1 and'2, these showthe application of'theinvention to an. inclinometer,

an .inclinometer.being, it will be understood, an instrument designedfor measuring theparallaxangle subtended at the instrument by a distantbase-and byv means of which'in gunnery. at .sea'.

the course of target can be determined.

Thetwoincoming beams of light from the two ends of the distant base aredenoted by. H and..l.8.' These entera prism combination D whichcomprises a light transmitting; and reflecting screen. IS. The two beamsof light emerging from the prism combination, each made up of atransmitted portion and a reflected portion, pass through objectives 20and are directed by reflecting prisms 2| into binocular eyepiece systems E These beams, as shown emerging from the prism combination D inFigure 1, may be regarded as in the plane of the paper. In one of thebeams emerging from the prism combination D there is a step prism 22adapted to displace or step that beam out of the plane of the paper intoa parallel plane, see Figure 2, to bring it into line with the left handeyepiece system E the associated objective 20 and prism 2| beingcorrespondingly displaced laterally relatively to those for the righthand eyepiece. A pair of prisms 23 rotatable in opposite senses aboutthe axis of the incoming beam 18 are provided to effect imagedisplacement for measuring purposes.

Figure 3 shows the upper part of a binocular periscope system adaptedfor estimation of range on the overlapping image principle. The opticalsystem comprises a prism combination made up of two prisms D and D witha light transmitting and reflecting screen 24 between them. Two beams oflight 25 and 26 are received by reflecting prisms '2'! and directeddownwards through objectives 28 to the prisms D and 13 each of which hasa lens 29 cemented on its entrance face. The action of the prismcombination will be clear. A part of each of the beams 25, 26, isreflected at the screen 24 and a part transmitted so that two beamsemerge from the prism combination, each comprising the reflected portionof one beam and the transmitted portion of the other beam 25, 28. Foreffecting image displacement for measuring purposes, various means maybe adopted. For example, the prisms 21 may be capable of differentialrotation.

3 In another arrangement a pair of prisms 30 are provided in one of thebeams, these being rotatable in opposite senses about the axis of thatbeam. As a still further alternative, there may be a deviating prism 3|,movable along the beam.

We are aware that it has been proposed to construct a binocular rangefinder of the coincidence type in which each of the two beams of lightfrom opposite ends of the base passes through two objectives, which arespaced apart, and through a half-opaque and half-transparent projectorlens situated between the objectives and intended to give halving of theimages, whereafter the beam is directed on to a semi-transparent screenwhere each beam is partly transmitted and partly reflected, thereflected portion of the one beam and the transmitted portion of theother beam being directed to one of the binocular eyepieces and thetransmitted portion of the first beam and the reflected portion-of thesecond beam being directed to the second eyepiece. In view of themultiplicity of air/glass surfaces, the loss of light in such anarrangement would be very high.

I claim:

A binocular range-estimating periscope operating on the overlappingimage principle and comprising binocular eyepieces, two top reflectorsto receive and reflect downwards two beams of light from a distantobject, an objective in the downward path of each of said beams, and aprism combination made up of two h'alves symmetrical about a verticalplane, on which plane in the interior of the combination there is areflecting-transmitting optical surface, the prism combination alsohaving a horizontal entrance face and a horizontal exit face, and, ineach half, between said entrance and exit faces, two oblique reflectingfaces one above the other, the path of each downwardly directed beambeing into one half of the combination at the entrance face, thenmeeting the upper oblique reflecting face of that half, then inwards tothe reflectingtransmitting surface where some of the light is reflectedoutwards to the lower oblique face of that half and thence to oneeyepiece, and some of the light is transmitted to the lower oblique faceof the other half and thence to the other eyepiece, the reflected andtransmitted portion combining to form overlapping images in the field ofeach eyepiece.

J. MARTIN STRANG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,813,673 Mihalyi July 7, 19312,098,917 Gunther Nov. 9, 1937 1,062,166 Konig May 20, 1913 1,108,180Jacob Aug. 25, 1914 1,021,306 Eppenstein Mar. 26, 1912 1,148,222Eppenstein July 27, 1915 2,106,632 Freund Jan. 25, 1938 2,290,864 ChurchJuly 28, 1942 2,315,783 Gilmore Apr. 6, 1943 FOREIGN PATENTS NumberCountry Date 674,777 Germany Apr. 21, 1939

